Wireless terminal and method of operating

ABSTRACT

A wireless terminal can communicate with a first network of first type and a second network of second different type. The wireless terminal performs a packet-domain attachment to the first network and initiates a ready timer indicating that the wireless terminal is in an attached state and has recently sent data to the first network. The wireless terminal initiates an inter-system change from the first network to the second network whereby the wireless terminal becomes registered to the second network. Advantageously the wireless terminal has means for rendering the ready timer ineffective when the inter-system change is performed. The network apparatus has means for initiating its own ready timer dependent on the attachment occurring, this ready timer also indicating that the wireless terminal is in an attached state and has recently sent data to the first network.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/902,365 filed Feb. 22, 2018, which is a continuation of U.S.application Ser. No. 14/390,933 filed Oct. 6, 2014 (now U.S. Pat. No.9,924,429 issued Mar. 20, 2018), which is a National Stage ofInternational Application No. PCT/JP2013/058466 filed Mar. 15, 2013,which claims priority from United Kingdom Patent Application No.1206790.6, filed Apr. 18, 2012, the contents of all of which areincorporated herein by reference.

TECHNICAL FIELD

The invention relates to a wireless terminal and method of operating,and in particular to intersystem change between E-UTRAN (also known asLTE) and GERAN.

BACKGROUND ART

In GPRS (General Packet Radio Service), as described in 3GPP TS 23.060,the UE (User Equipment) can be in three different modes or states:

In GPRS IDLE state, the wireless terminal (mobile station, MS or UserEquipment, UE) of a subscriber is not attached to GPRS mobilitymanagement (MM) of the network. The wireless terminal and Serving GPRSSupport Node (SGSN) contexts hold no valid location or routinginformation associated with the subscriber.

In STANDBY state, the subscriber is attached to GPRS mobilitymanagement. The wireless terminal (UE) and SGSN have established GPRSmobility management (GMM) contexts.

In READY state, the SGSN MM context corresponds to the STANDBY MMcontext extended by location information associated with the subscriberon the cell level. The wireless terminal (UE) performs mobilitymanagement procedures to provide the network with the actual selectedcell. GPRS cell selection and re-selection is generally done locally bythe wireless terminal (UE), or may optionally be controlled by thenetwork.

Regardless of whether a radio resource is allocated to the subscriber ornot, the GMM context remains in the READY state even when there is nodata being communicated. A timer (GMM READY timer T3314) supervises theREADY state. The GMM READY timer is initiated or started when data issent by the UE and the wireless terminal goes into the READY state. AGMM context moves from READY state to STANDBY state when the GMM READYtimer expires. In order to move from READY state to IDLE state, thewireless terminal (UE) initiates the GPRS Detach procedure. More detailscan be found in 3GPP TS 23.060, sub-clause 6.1.1. The length (henceduration) of the GMM READY timer can only be changed by the SGSN.

For intersystem change between UTRAN and GERAN, the GMM READY timerT3314 can be kept running due to Cell Change Order (CCO) procedurecompletion, as described in 3GPP TS 44.060, sub-clause 8.4.1:

“In case of inter-RAT network controlled cell reselection, the mobilestation shall regard the network controlled cell re-selection assuccessfully completed according to specifications of the target RAT, orwhen the GMM READY timer (see 3GPP TS 24.008) stops running during theexecution of the procedure. The mobile station shall then stop timerT3174.”

It should be noted that 3GPP TS 23.060, sub-clause 6.13.1.1, whichdescribes Iu mode to A/Gb mode Intra SGSN Change, only requires that theUE checks the PMM state in UTRAN to decide which procedure to triggerafter intersystem change from UTRAN to GERAN, i.e. there is no checkingof the Ready timer due to an intersystem change from UTRAN to GERANbeyond the case of the CCO procedure completion as highlighted above.

Evolved UTRAN (E-UTRAN) specifies an Idle mode Signalling Reduction(ISR) function which provides a mechanism to limit or reduce signallingin idle mode during any inter-RAT cell-reselection between E-UTRAN andUTRAN/GERAN. By keeping a context for a wireless terminal (UserEquipment, UE) in both the MME and the SGSN, the UE does not need toperform NAS registration procedure (Routing Area Update, RAU) whenmoving between E-UTRAN and GERAN/UTRAN as long as the UE stays in theregistered areas (Routing Area in GERAN/UTRAN, tracking Area List inE-UTRAN).

According to this mechanism the UE in idle mode, when ISR is activated,is registered with both the MME of the E-UTRAN and the SGSN of theUTRAN/GERAN (see 3GPP TS23.401, Annex J1). Both the SGSN and the MMEhave a control connection with the serving gateway (S-GW).

The UE receives and stores mobility management (MM) parameters providedto the UE by the SGSN (e.g. P-TMSI and RA) and provided to the UE by theMME (e.g. GUTI and TA(s)) and the UE stores session management (bearer)contexts that are common to E-UTRAN and GERAN/UTRAN accesses.

Using these stored parameters and contexts, the UE when it is in idlestate can reselect between E-UTRAN and GERAN/UTRAN radio access cellswhen the UE is within the registered routing areas (RAs) and trackingareas (TAs) without any need to perform any tracking area update (TAU)or routing area update (RAU) procedures by interacting with the network.

CITATION LIST Non Patent Literature

NPL 1: 3GPP TS 23.060 V11.0.0 (2011-12)

NPL 2: 3GPP TS 23.401 V11.0.0 (2011-12)

NPL 3: 3GPP TS 44.060 V11.0.0 (2012-03)

SUMMARY OF INVENTION Technical Problem

In existing 3GPP specifications, the handling of the Ready timer is notspecifically described for the case of an intersystem change betweenE-UTRAN and GERAN. However, it has now been realised that twoproblematic scenarios will occur during idle mode cell reselection,depending on whether or not ISR is activated or not activated. These twoscenarios will now be described with reference to FIG. 1, FIG. 2 (for afirst scenario) and FIG. 3 (for a second scenario).

FIGS. 1 and 2, are event diagrams according to a first scenario in whichISR is activated when the UE reselects GERAN.

FIG. 1 illustrates current procedure for performing an E-UTRAN-to-GERANintersystem change while Ready timer is running and ISR is activatedwhen the UE reselects GERAN, where ISR has been previously activatedwhile the UE 102 was in GERAN. In this first case, when a UE 102 withReady timer running selects E-UTRAN (by the known ‘re-selection’procedure 110), performs TAU 112, and then goes back to (selects) GERAN(see block 118) with Ready timer still running, the UE will perform aCell Update procedure 120 once in GERAN even though the UE comes back tothe registered RA. This is because the Cell Update is triggered byexpiry of the Ready timer, as shown by arrow 122.

FIG. 2 is another event diagram according to the first scenario (ISRhaving been activated), illustrating current procedure for performing anE-UTRAN-to-GERAN intersystem change while Ready timer is running and ISRis activated when the UE reselects GERAN, where ISR has been previouslyactivated while the UE was in E-UTRAN and not in GERAN. In this secondcase, following the TAU request 112 from the UE 102, a context request224 is transmitted by the MME 106 to the SGSN 104, and a contextresponse 226 is transmitted by the SGSN 104 to the MME 106, in responseto the context request 224.

It can be seen from FIG. 1 and FIG. 2 that keeping Ready timer runningwill introduce additional signalling in the form of a cell update 120.However, since ISR is activated when the UE reselects GERAN, the GERANnetwork does not expect any signalling from the UE at intersystemchange, so this extra cell update 120 is unwanted and unnecessary.

FIG. 3 illustrates a second scenario in which ISR is not activated whenthe UE reselects GERAN. When the UE 102 with Ready timer running (122)selects E-UTRAN (block 110), performs TAU 112, 117. Following the TAUrequest 112 from the UE 102, a context request 224 is transmitted by theMME 106 to the SGSN 104, and a context response 226 is transmitted bythe SGSN 104 to the MME 106, in response to the context request 224. TheUE then goes back to GERAN (see block 119). The UE 102 will perform aRouting Area Update procedure 328, 330 when the UE 102 comes back to theregistered RA (block 119).

For this second scenario, it can be seen from FIG. 3 that keeping theReady timer running while the UE is in E-UTRAN serves no useful purposesince the UE will, by default, perform a Routing Area Update procedure328, 329 once the UE is back in GERAN. Additionally, keeping the Readytimer running is a waste of resources while the UE is in E-UTRAN, forboth the UE and the network.

It is clearly desirable to overcome the above-described problems andlimitations of the current state of the art.

It is an object of the invention to provide improved operation of thewireless terminal at intersystem change from one type of network toanother type of network, in particular from E_UTRAN to UTRAN/GERAN.

Solution to Problem

According to one aspect of the invention, there is provided a wirelessterminal for communicating with a first network of first type and forcommunicating with a second network of second type different than thefirst type, the wireless terminal comprising: means for performing anattachment to the first network in a packet domain and initiating aready timer dependent on the performing the attachment, the ready timerindicating that the wireless terminal is in an attached state; means forinitiating an inter-system change from the first network to the secondnetwork whereby the wireless terminal becomes detached from the firstnetwork and attached to the second network in the packet domain; andmeans for rendering ineffective the ready timer depending on theinitiated inter-system change.

According to another aspect of the invention there is provided a methodfor use in wireless terminal, the wireless terminal being forcommunicating with a first network of first type and for communicatingwith a second network of second type different than the first type, themethod comprising: performing an attachment to the first network in apacket domain and initiating a ready timer dependent on the performingthe attachment, the ready timer indicating that the wireless terminal isin an attached state; initiating an inter-system change from the firstnetwork to the second network whereby the terminal becomes detached fromthe first network and attached to the second network in the packetdomain; and rendering ineffective the ready timer depending on theinitiated inter-system change.

According to another aspect of the invention there is provided acomputer program product for use in wireless terminal for communicatingwith a first network of first type and for communicating with a secondnetwork of second type different than the first type, the computerprogram product comprising: a processor; and memory coupled to theprocessor, the memory comprising instructions which when carried out bythe processor perform the functions of: performing an attachment to thefirst network in a packet domain and initiating a ready timer dependenton the performing the attachment, the ready timer indicating that thewireless terminal is in an attached state; initiating an inter-systemchange from the first network to the second network whereby the terminalbecomes detached from the first network and attached to the secondnetwork in the packet domain; and rendering ineffective the ready timerdepending on the initiated inter-system change.

According to another aspect of the invention there is provided a networkapparatus for operating as part of a first network of first type and forcommunicating with a wireless terminal that can communicate with asecond network of second type different than the first type, the networkapparatus comprising: means for performing an attachment to the wirelessterminal in a packet domain and initiating a ready timer in the networkapparatus dependent on the performing the attachment, the ready timerindicating that the wireless terminal is in an attached state; meansfor, during an inter-system change of the wireless terminal from thefirst network to the second network, performing a detachment whereby thewireless terminal becomes detached in the packet domain from the firstnetwork; and means for rendering ineffective the ready timer dependingon the performing a detachment.

According to another aspect of the invention there is provided a methodfor use in a network apparatus, the network apparatus being foroperating as part of a first network of first type and for communicatingwith a wireless terminal that can communicate with a second network ofsecond type different than the first type, the method comprising:performing an attachment to the wireless terminal in a packet domain andinitiating a ready timer in the network apparatus dependent on theperforming the attachment, the ready timer indicating that the wirelessterminal is in an attached state; during an inter-system change of thewireless terminal from the first network to the second network,performing a detachment whereby the wireless terminal becomes detachedin the packet domain from the first network; and rendering ineffectivethe ready timer depending on the performing a detachment.

According to another aspect of the invention there is provided acomputer program product for use in a network apparatus, the networkapparatus being for operating as part of a first network of first typeand for communicating with a wireless terminal that can communicate witha second network of second type different than the first type, thecomputer program product comprising: a processor; memory coupled to theprocessor and comprising instructions which when carried out by theprocessor perform the functions of: performing an attachment to thewireless terminal in a packet domain and initiating a ready timer in thenetwork apparatus dependent on the performing the attachment, the readytimer indicating that the wireless terminal is in an attached state;during an inter-system change of the wireless terminal from the firstnetwork to the second network, performing a detachment whereby thewireless terminal becomes detached in the packet domain from the firstnetwork; and rendering ineffective the ready timer depending on theperforming a detachment.

Advantageous Effects of Invention

When implemented for use in E-UTRAN and UTRAN/GERAN networks, theinventive features provide the advantage that unnecessary handling ofReady timer is avoided while the UE is in E-UTRAN. Also Cell Updatesignalling is avoided when the UE re-selects to GERAN when ISR isactivated.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrate a known procedure for performing an E-UTRAN-to-GERANintersystem change while Ready timer is running and ISR is activatedwhen the UE reselects GERAN.

FIG. 2 illustrate a known procedure for performing an E-UTRAN-to-GERANintersystem change while Ready timer is running and ISR is activatedwhen the UE reselects GERAN.

FIG. 3 illustrates a known procedure for performing an E-UTRAN-to-GERANintersystem change while Ready timer is running and ISR is not activatedwhen the UE reselects GERAN.

FIG. 4 is an event diagram showing proposed new methods for performingE-UTRAN to GERAN intersystem change while Ready timer is running and ISRis activated when the UE reselects GERAN.

FIG. 5 is an event diagram showing proposed new methods for performingE-UTRAN to GERAN intersystem change while Ready timer is running and ISRis activated when the UE reselects GERAN.

FIG. 6 is an event diagram showing a proposed new method for performingE-UTRAN to GERAN intersystem change while Ready timer is running and ISRis not activated when the UE reselects GERAN.

FIG. 7 shows a wireless terminal and network apparatus arranged foroperating according to the invention.

DESCRIPTION OF EMBODIMENTS

Embodiments, described herein, provide that:

Firstly, the UE ignores Ready timer once it has moved to E-UTRAN (i.e.it has connected to the E-UTRAN). This can be done via the followingthree alternative implementations:

the UE ignores the ready timer after initiation of an intersystemchange, or

the UE stops Ready timer when moving to E-UTRAN, or

the UE stops Ready timer when moving from E-UTRAN to GERAN.

In case the UE ignores the ready timer after intersystem change, the UEmay ignore the expiry/termination/stopping of the Ready timer. Inaddition, the UE may ignore the ready timer prior to, and until, itsexpiration.

Optionally, the network (SGSN) can ignore its own Ready timer. In casethe UE stops Ready timer the usual behaviour would apply, i.e. the UEwould start again the periodic routing area update timer T3312.

Secondly, the SGSN stops Ready timer associated with the UE when theSGSN knows the UE has moved to E-UTRAN (LTE), i.e. when the SGSNreceives a Context Request from the MME (this occurring when ISR has notbeen activated while the UE was in GERAN).

When the SGSN stops the Ready timer the usual behaviour would apply,i.e. the SGSN would start again the mobile reachable timer (see TS23.060). Then, as per TS 23.060 subclause 8.1.3a, if PDP Contextsassociated with the UE are to be preserved, the SGSN shall send aRelease Access Bearers Request to the serving gateway (S GW) to removethe SGSN address for user plane and downlink S4 GTP-U TEID.

FIG. 4 is an event diagram showing a proposed new method for performingE-UTRAN to GERAN intersystem change while Ready timer is running and ISRis activated when the UE reselects GERAN, when ISR has been previouslyactivated while the UE was in GERAN. The Ready timer is stopped (box440) in response to the UE selecting E-UTRAN (box 110).

FIG. 5 is another event diagram showing a proposed new method forperforming E-UTRAN to GERAN intersystem change. This method is carriedout while Ready timer is running and ISR is activated, when the UEreselects GERAN, by means of the tracking area updating accept message116, when ISR has not been previously activated while the UE waspreviously in GERAN (box 109). As in FIG. 4, The Ready timer is stopped(box 440) in response to the UE selecting E-UTRAN (box 110). The timermay be stopped in response to the sending of the tracking area update(112). Alternatively or in addition, as shown by box 550, the SGSN 104may stop its own Ready timer in response to its receiving a CONTEXTREQUEST 224 sent by the MME 106. Because there is no expiry of the Readytimer in the wireless terminal or the SGSN, no Cell Update is performed(442).

FIG. 6 is another event diagram showing a proposed new method forperforming E-UTRAN to GERAN intersystem change. This method is carriedout while Ready timer is running and ISR is not activated (117). Whenthe UE re-selects GERAN (box 119), because ISR is not activated, the UEperforms a RAU procedure by sending a RAU REQUEST message 328, and theSGSN responds by sending a RAU ACCEPT message 330.

FIG. 7 shows a wireless terminal 710 comprising a receiver 712, atransmitter 714, a processor 716 coupled to the receiver 712 and to thetransmitter 714, and a memory 718 coupled to the processor 716. Theprocessor 716 is configured to control the receiver 712 and thetransmitter 714 according to instructions contained in the memory 718.

The receiver 712 of the wireless terminal 710 is arranged for receiving,via a wireless link 742 between the wireless terminal and the networkapparatus, signalling data and/or traffic/media data transmitted by anetwork apparatus 720. The transmitter 714 of the wireless terminal 710is arranged for transmitting signalling data and/or traffic/media datavia a wireless communication link 744 between the wireless terminal andthe network apparatus and is preferably arranged for performingtransmission of information intended for one or more other networkapparatus (not shown) via one or more other wireless links (not shown).

The communications link 742 used by the receiver 712 of the wirelessterminal 710 and the communication link 744 used by the transmitter 714of the wireless terminal 710 can be considered as the same communicationlink. Alternatively, the wireless communication link 742 used by thereceiver 712 of the wireless terminal 710 can be considered as one linkand the wireless communication link 744 used by the transmitter 714 ofthe wireless terminal 710 can be considered as another communicationlink. For example, the link 742 used by the receiver 712 can beconsidered as a down link and the link 744 used by the transmitter 714can be considered as an uplink. Such use of communication links fortransmitting and receiving signals are well known in the art and neednot be discussed further.

The network apparatus 720 comprises a receiver 722, a transmitter 724, aprocessor 726, and a memory 728. The functions of the receiver 722,transmitter 724, processor 726 and memory 728 of the network apparatus720 are similar to the respective functions of the receiver 712,transmitter 714, processor 716 and memory 718 of the wireless terminal710. In use, the network apparatus 720 wirelessly transmits, via itstransmitter 724 and wireless link 742, signals that are intended for thereceiver 712 of the wireless terminal 710. Similarly the transmitter ofwireless terminal 710 transmits one or more signals wirelessly that areintended for the network apparatus 720 via transmitter 714 and wirelesslink 744.

Preferably the receiver 712 of the wireless terminal 710 can receivesignals transmitted by one or more further network apparatus (notshown). Similarly, preferably the transmitter 714 of the wirelessterminal 710 can transmit signals intended for one or more furthernetwork apparatus (not shown).

Preferably the receiver 222 of the network apparatus 720 can receivesignals transmitted by one or more further wireless terminals (notshown). Similarly, preferably the transmitter 724 of the networkapparatus 720 can transmit signals intended for one or more furtherwireless terminal(s) (not shown).

In this example the network apparatus 720 forms part of a base stationof a cellular communications network and the wireless terminal 710 is acellular wireless terminal. However, it should be understood there mayexist only two devices, illustrated as the wireless terminal 710 and thenetwork apparatus 720 in FIG. 3. A wireless communication systemcomprising only two such devices or a small number of devices canbenefit from the claimed features.

A base station controller (BSC) 730, coupled to the network apparatus720, is arranged to route signals to/from the network apparatus 720 andto/from other such network apparatus (not shown). A mobile switchingcentre (MSC) 740 is arranged to route signals to/from the base stationcontroller 730 and to/from other such base station controllers (notshown). A MME or SGSN 750 (depending on whether the network is E-UTRANor UTRAN/GERAN) is arranged to control and route signals to/from themobile switching centre 740 and to/from a public switched telephonenetwork (PSTN) (not shown). The principles of operation of the basestation controller 730, mobile switching centre 740 and MME or SGSN 750are well known and need not be described further.

The above-described embodiments are applicable to E-UTRAN (as the secondnetwork) and UTRAN/GERAN (as the first network, where the Activate PDPcontext request message of GERAN is an equivalent of the PDNconnectivity request message of E-UTRAN). Clearly, the embodiments canbe applied, with minor simple modification as required, to other RANtechnologies.

As can be seen from FIG. 4, the UE will not perform unnecessary cellupdates when ISR is activated. Otherwise the benefits from ISR would belost.

As can be seen from FIG. 6, the UE will not maintain any Ready timerunnecessarily when ISR is not activated. Indeed, when ISR is notactivated the UE will perform RAU at intersystem change from E-UTRAN toGERAN.

On the network side, the network does not need to maintain Ready timerfor the UE if the UE has moved to E-UTRAN, which the network knows sincethe UE will always perform a TAU when moving from GERAN to E-UTRAN, ifReady timer is running in the UE, as per the following requirementreproduced from 3GPP TS 24.301 release 11.2.1, subclause 5.5.3.2.2:

-   -   “The UE in state EMM-REGISTERED shall initiate the tracking area        updating procedure by sending a TRACKING AREA UPDATE REQUEST        message to the MME, [ . . . ]    -   1) when the UE reselects an E-UTRAN cell while it was in GPRS        READY state or PMM-CONNECTED mode;”

which is also described in 3GPP TS 23.401, version 11.1.0, subclause5.3.3.0, a portion of which is reproduced below:

-   -   “A standalone tracking area update (with or without S GW change,        described in clauses 5.3.3.1 and 5.3.3.2 respectively) occurs        when a GPRS-attached or E UTRAN-attached UE experiences any of        the following conditions:    -   UE detects it has entered a new TA that is not in the list of        TAIs that the UE registered with the network (except for the        case of a UE configured to perform Attach with IMSI when        entering a TA in a new non-equivalent PLMN in RRC-IDLE mode);    -   the periodic TA update timer has expired;    -   UE was in UTRAN PMM_Connected state (e.g. URA_PCH) when it        reselects to E UTRAN;    -   UE was in GPRS READY state when it reselects to E UTRAN;”

It follows that, as depicted on FIG. 6, the SGSN can stop its Readytimer for the UE once the SGSN receives a Context Request message fromthe MME.

The above-described embodiments provide that, in a UE supporting GPRSand LTE, the Ready timer is rendered ineffective by being stopped:

-   -   at intersystem change from GERAN to E-UTRAN (GPRS to LTE), or    -   at intersystem change from E-UTRAN to GERAN (LTE to GPRS).

According to another variant, the UE would ignore the Ready timer afterintersystem change from LTE to GPRS, thus rendering the Ready timerineffective. Clearly, according to each embodiment, the Ready timer isrendered ineffective.

Preferably, in an SGSN, the Ready timer is stopped or ignored by theSGSN when the SGSN receives the indication that the UE performs TAU.That is, when the SGSN receives the tracking area updating request, orthe context request (following a tracking area updating request from theUE to the MME). Again in this case, the Ready timer is renderedineffective.

As can be seen in the excerpts below from 3GPP TS 24.008, currentlyaccording to the state of the art, the only condition to stop Readytimer, on both the UE side and the network side, is the indication of“Forced to Standby”.

3GPP TS 24.008, section 11.2.2, Table 11.3a (GPRS Mobility managementtimers—MS side), fourth row, indicates in relation to the T3314 READYtimer (A/Gb mode only):

-   -   Default timer value is 44 seconds, for all states except        GMM-DEREG. Cause of start of timer is transmission of a PTP PDU.        The normal stop is “Forced to Standby”. On expiry of the T3314        timer, no cell-updates are performed.    -   Note 2: The default value of this timer is used if neither the        MS nor the Network send another value, or if the Network sends        this value, in a signalling procedure.

3GPP TS 24.008, section 11.2.2, Table 11.4a (GPRS Mobility managementtimers—network side), third row, states that:

-   -   T3314 READY timer (A/Gb mode only) value is “Default 44 seconds        for all STATEs except GMM-DEREG. Cause of start of timer T3314        is “Receipt of a PTP PDU”.    -   The normal stop is “Forced to Standby”. On expiry of the T3314        timer, the “network shall page the MS if a PTP PDU has to be        sent to the MS.”    -   Note 2: The default value of this timer is used if neither the        wireless terminal (UE) nor the Network send another value, or if        the Network sends this value, in a signalling procedure. The        value of this timer should be slightly shorter in the network        than in the wireless terminal (UE), this is a network        implementation issue.

It follows that rendering the Ready timer ineffective at a system changebetween GERAN and E-UTRAN therefore represents a novel feature thatovercomes an unforeseen problem.

In the accompanying drawings, FIGS. 1-3 illustrate operation of awireless terminal according to known methods and FIGS. 4-6 illustratenovel operation of a wireless terminal and a network apparatus accordingto inventive features described herein. FIG. 7 applies to known methodsand the inventive features.

This software can be stored in various types of non-transitory computerreadable media and thereby supplied to computers. The non-transitorycomputer readable media includes various types of tangible storagemedia. Examples of the non-transitory computer readable media include amagnetic recording medium (such as a flexible disk, a magnetic tape, anda hard disk drive), a magneto-optic recording medium (such as amagneto-optic disk), a CD-ROM (Read Only Memory), a CD-R, and a CD-R/W,and a semiconductor memory (such as a mask ROM, a PROM (ProgrammableROM), an EPROM (Erasable PROM), a flash ROM, and a RAM (Random AccessMemory)). Further, the program can be supplied to computers by usingvarious types of transitory computer readable media. Examples of thetransitory computer readable media include an electrical signal, anoptical signal, and an electromagnetic wave. The transitory computerreadable media can be used to supply programs to computer through a wirecommunication path such as an electrical wire and an optical fiber, orwireless communication path.

Various other modifications will be apparent to those skilled in the artand will not be described in further detail here.

As mentioned above, although the present invention is explained withreference to the illustrative embodiment, the present invention is notlimited by the above. Various modifications understood by a personskilled in the art can be made within the scope of the invention.

This application is based upon and claims the benefit of priority fromUnited Kingdom patent application No. 1206790.6 filed on 18 Apr. 2012,the disclosure of which is incorporated herein in its entirety byreference.

INDUSTRIAL APPLICABILITY

The present invention relates to a wireless terminal and method ofoperating, and in particular to intersystem change between E-UTRAN (alsoknown as LTE) and GERAN.

REFERENCE SIGNS LIST

-   102 UE-   104 SGSN-   106 MME-   710 wireless terminal-   712 receiver-   714 transmitter-   716 processor-   718 memory-   720 network apparatus-   722 receiver-   724 transmitter-   726 processor-   728 memory-   730 BSC-   740 MSC-   742 wireless link-   744 wireless link-   750 MME/SGSN

The invention claimed is:
 1. A mobile station comprising: at least onememory storing instructions; and at least one processor configured toexecute the instructions to: perform an attachment to a first systemwhich is configured to operate in a first mode; communicate with thefirst system, wherein the first system is different from a second systemwhich is configured to operate in a second mode; start a timer based ontransmission of data; initiate a tracking area update procedure in acase where the mobile station performs an inter-system change from thefirst mode to the second mode; and stop the timer based on theinter-system change.
 2. The mobile station according to claim 1, whereinthe first mode comprises an A/Gb mode.
 3. The mobile station accordingto claim 1, wherein the first system comprises a GSM/EDGE Radio AccessNetwork (GERAN), and wherein the second system comprises an EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN).
 4. The mobilestation according to claim 1, wherein the timer is a General PacketRadio Service (GPRS) Mobility Management (GMM) ready timer.
 5. Themobile station according to claim 1, wherein the transmission of data istransmission of a Protocol Data Unit (PDU).
 6. A method for controllinga mobile station, the method comprising: performing an attachment to afirst system which is configured to operate in a first mode;communicating with the first system, wherein the first system isdifferent from a second system which is configured to operate in asecond mode, starting a timer based on transmission of data; initiatinga tracking area update procedure in a case where the mobile stationperforms an inter-system change from the first mode to the second mode;and stopping the timer based on the inter-system change.
 7. The methodaccording to claim 6, wherein the first mode comprises an A/Gb mode. 8.The method according to claim 6, wherein the first system comprises aGSM/EDGE Radio Access Network (GERAN), and wherein the second systemcomprises an Evolved Universal Terrestrial Radio Access Network(E-UTRAN).
 9. The method according to claim 6, wherein the timer is aGeneral Packet Radio Service (GPRS) Mobility Management (GMM) readytimer.
 10. The method according to claim 6, wherein the transmission ofdata is transmission of a Protocol Data Unit (PDU).